مجله دندانپزشکی دانشگاه علوم پزشکی تهران
سال بیستم شماره 3 (پیاپی 52، پاییز 1386)

Considering flexural strength of fiber-reinforced composites (FRC) and also the role of conservative cavities in protecting sound tissue of abutments, the aim of this study was to evaluate the fracture resistance of these bridges by handmade samples in vitro. In this experimental in vitro study, 44 sound newly extracted teeth were used to make 22 fixed inlay bridges including 11 three unit anterior upper inlay bridges substituting clinical model of upper central and 11 three unit posterior lower inlay bridges substituting clinical model of lower first molar. Specimens were prepared with FRC and mounted with artificial PDL in acryl. Cases were exposed to final load by using Universal Testing Machine (Instron 1195) with the speed of 1 mm/min. Statistical analysis was performed by Kolmogorov- Smirnov, independent sample T and Kaplan-Meier tests with p<0.05 as the level of significance. Based on the statistical tests, the 95% confidence interval of mean was 450-562 N in anterior and 1473- 1761 N in posterior area. Fracture strength was high in the studied groups. Fractures in both groups occurred on composite facing, and the framework remained intact. The highest percentage of fracture in posterior teeth was in the middle of pontic towards the distal connector and in the anterior teeth in the lateral connector, between central pontic and lateral abutment. Using the independent sample T test a significant statistical difference was observed between two groups (P<0.001). The fracture resistance of anterior samples was lower than the posterior ones. Based on the results of this study regarding the high fracture resistance in both areas FRC inlay bridges could be recommended for upper anterior and lower posterior teeth in clinical dentistry certainly more studies are needed to ascertain this treatment option.

Complete obturation of the prepared root canal is an essential step in endodontic treatment. Combination of gutta-percha and a sealer is widely used in clinical practice for root canal obturation, thus microleakage studies on sealing properties of these materials constitute an important part of endodontic researches. The aim of this study was to evaluate the microleakage of three root canal sealers: Apexit, AH26 and Dorifill by electrochemical method. In this experimental study, 55 extracted human maxillary and mandibular cuspids were used. The coronal part of teeth were removed and the root canals were prepared using the step-back technique. The specimens were randomly divided into 3 groups of 17 samples each. Teeth in each group were filled with one of the sealers and gutta-percha by lateral condensation technique. 4 specimens served as positive and negative controls. An electrochemical method was used for evaluation of apical leakage with the electrical source potential of 10 V. Measurements of current flow through the test system were recorded every 72 hours. Data were analyzed by Kruskall Wallis and Mann Whitney tests. P<0.05 was considered as the level of significance. All specimens of the three groups showed low initial leakage that increased during the test period. The mean leakage in Apexit group was higher than AH26 and Dorifill groups. The lowest mean leakage was related to Dorifill group. Although no statistically significant difference was observed between this sealer and AH26. The results of this study revealed that the best apical seal was obtained using Dorifill and AH26 sealers. The poorest result was observed in Apexit.

Replacing fractured ceramometal restorations may be the best treatment option, but it is costly. Many different bonding systems are currently available to repair the fractured ceramometal restorations. This study compared the shear bond strength of composite to a base metal alloy using 4 bonding systems. In this experimental in vitro study, fifty discs, casted in a Ni-Cr-Be base metal alloy (Silvercast, Fulldent),were ground with 120, 400 and 600 grit sandpaper and divided equally into 5 groups receiving 5 treatments for veneering. Conventional feldspathic porcelain (Ceramco2, Dentsply Ceramco) was applied on control group (PFM or group1) and the remaining metal discs were air- abraded for 15 seconds with 50 mm aluminum oxide at 45 psi and washed for 5 seconds under tap water.Then the specimens were dried by compressed air and the groups were treated with one of the bonding systems as follows: All-Bond 2 (AB), Ceramic Primer (CP), Metal Primer II (MP) and Panavia F2 (PF). An opaque composite (Foundation opaque) followed by a hybrid composite (Gradia Direct) was placed on the treated metal surface and light cured separately. Specimens were stored in distilled water at 370C and thermocycled prior to shear strength testing. Fractured specimens were evaluated under a stereomicroscope. Statistical analysis was performed with one way ANOVA and Tukey HSD tests. P<0.05 was considered as the level of significance. Mean shear bond strengths of the groups in MPa were as follows: PFM group 38.6±2, All-Bond 2 17.06±2.85, Ceramic Primer 14.72±1.2, Metal Primer II 19.04±2.2 and Panavia F2 21.37±2.1. PFM group exhibited the highest mean shear bond strength and Ceramic Primer showed the lowest. Tukey's HSD test revealed the mean bond strength of the PFM group to be significantly higher than the other groups (P<0.001). The data for the PF group was significantly higher than AB and CP groups (P<0.05) and the shear bond strength of the MP group was higher than CP group, but was not significantly different from AB (P>0.05). Based on the results of this study, the most reliable treatment for fractured metal-ceramic restorations would be the replacement of the restoration. If this is not possible, adhesive resin cements containing filler and phosphate-based monomers (especially MDP) such as Panavia F2 could be recommended for bonding composite to base metal alloys.

Accurate measurement of bone height and width is essential prior to dental implant placement. The method of surgery as well as, the type and size of implants are determined according to dimensions of the residual bone. The purpose of this study was to evaluate the accuracy of linear tomography in localization of the floor of nasal fossa and maxillary sinus, and to determine the width of maxillary bone at the designated site for implant placement. In this test evaluation study, the vertical distances between the alveolar crest and the floor of nasal fossa and the floor of maxillary sinus was measured by the tomographic slices in 12 sites of three dry human skulls. In addition, the width of maxillary bone was measured at the same slices. The skulls were then sectioned through the marked places. Then the radiographic values were compared with the real values of bone sections. After correction of tomographic values by the magnification factor of the unit, the mean absolute measurement error for vertical values at nasal fossa and maxillary sinus area in tomographic slices were 0.28 mm (SD= 0.24) and 1.1 mm (SD= 0.68) respectively. The mean absolute measurement error for maxillary width at the nasal fossa and maxillary sinus area were 0.65 mm (SD= 0.50) and 0.55 mm (SD= 0.45) respectively. 100 % of vertical values at nasal fossa area and 50 % of vertical values at maxillary sinus area were within ± 1 mm error limit. In addition, 50 % of width measurements at nasal fossa area and 83.3 % at maxillary sinus area were within ± 1 mm error limit. The linear tomography is more accurate in height estimation at nasal fossa area and in width estimation at maxillary sinus area. The accuracy of linear tomography in height and width estimation is within acceptable limits at both nasal fossa and maxillary sinus area.

Root filling materials are usually in close contact with living tissues. So their biological properties like mutagenicity and cytotoxicity are important. These properties help us determine the potential damage to periapical tissues, or potential DNA mutations, and malignant transformation of the cells. The aim of this study was to evaluate the mutagenicity and cytotoxicity of four root canal sealers: AH Plus (Dentsply, DeTrey), Ketac-Endo Aplicap (3M ESPE), Sankin Apatite III (Sankin K.K), and Tubli-Seal EWT (Kerr). In this experimental in vitro study fresh and set specimens from AH Plus, Ketac-Endo Aplicap, Sankin Apatite III, and Tubli-Seal EWT were immersed in culture medium for 1, 2 and 7 days. Cytotoxicity was assessed using tetrazolium bromide reduction assay (MTT) after 1, 2 and 7 days exposure of diluted extracts to L929 cells. Extracts of sealers in phosphate buffer saline (PBS) were used to examine the mutagenic effects by sos-umu test according to standard procedures. Data were analyzed using one way ANOVA, Kruskall Wallis, Mann Whitney and Post hoc tests with P<0.05 as the level of significance. Extracts of all freshly mixed sealers were cytotoxic. Ketac-Endo Aplicap and Sankin Apatite III showed the lowest toxicity respectively and Tubli-Seal EWT the highest. In contrast to other sealers, the cytotoxicity of Tubli-Seal showed no decrease with time. -galactosidase did not increase significantly thus none of the sealers showed mutagenic effects. Based on the results of this study, Tubli-Seal EWT showed the highest cytotoxicity with time. Other sealers showed decreasing cytotoxicity with time. No mutagenicity effects was observed in none of tested materials.

Functional appliances refer to a variety of removable or fixed appliances designed to alter the mandibular position both sagitally and vertically, resulting in orthodontic and orthopedic changes. Despite the long history of functional appliances, there is still much controversy related to their effectiveness and mode of action. The aim of this study was to evaluate dental and skeletal effects of Fa II in patients with class II malocclusion due to mandibular deficiency. In this before-after clinical trial, 35 patients with class II div I malocclusion were selected. These samples were under treatment with Fa II appliance for 11 months. The range of age of females was 10-13 years and males 11-14 years. Combination analysis was used to determine skeletal and dental effects. Paired t-test was used to compare the differences of mean value pre and post treatment. P<0.05 was considered as the level of significance. There was significant difference between pre and post treatment in respect to posterior and anterior facial height, eruption of upper and lower posterior teeth, eruption of upper anterior teeth, mandibular body length, ANB angle, IMPA and 1 to SN. No significant difference was observed between pre and post treatment regarding facial growth. Treatment with Fa II functional appliance leads to significant alterations in dental and skeletal elements of craniofacial complex and improvement of dental and jaws relationship.

The goal of dental treatment is to improve oral hygiene, to maintain teeth and minimize the risk of diseases. Although data obtained from radiographs has distinct advantages to patients, the radiation side effects should be considered as well. FDA has developed a guideline for prescribing radiographs in the middle of the eighties. The aim of this study was to evaluate the reasons of ordering panoramic radiographs and their accordance with FDA guidelines in Tehran dental school. This descriptive study was carried out on 250 patients referred from different departments of Tehran dental school to radiology department for panoramic radiography. Chief complaints and clinical findings of patients were recorded in a check list and compared with the FDA guidelines prescribed. Our findings showed that prescription of panoramic radiographs were in accordance with FDA guidelines in 97.2% of cases. Based of the results of this study, the trend of panoramic radiography ordering in the dental school of Tehran university is adequate. This may be attributed to the academic field of this study.

Incomplete root development caused by trauma, caries, or pulpal pathosis requires special attention and treatment. Although calcium hydroxide apexification has been used successfully for years but it requires patient cooperation and multiple appointments. Single visit apexification with MTA has been used in recent years. The purpose of this study was to compare bacterial microleakage of two types of MTA (Made in Iran and Brazil) applied as apical barrier in open apex teeth. 48 single root teeth were used in this experimental in vitro study. Teeth apices were prepared as open apex teeth. For canal obturation the 4mm of root end was filled with 2 types of MTA (white Iranian MTA salami co. Iran and Angelus MTA Angelus Brazil) from coronal access. Teeth were mounted in self-cured acryl and put in BHI microbial culture. A suspension of Staphylococcus epidermidis was injected from coronal area into the root canals.The teeth were incubated and examined every 24 hours for microbial microleakage, indicated as turbidity in culture. Data were analyzed using Fisher exact test with p<0.05 as the level of significance. Microleakage appeared after 15 days in all Iranian and after 17 days in Angelus MTA samples.There was no significant difference between microleakage of two types of MTA (P = 0.48). Based on the results of this study, there was no significant difference between microleakage of Iranian and Angelus MTA. If further studies confirm other physical, chemical, biological and sealing properties of Iranian MTA, it could be recommended for clinical application

Bleaching products as chemical materials can exert side effects on soft and hard tissues and existing restorative materials with oxidizing mechanism. The aim of this study was to evaluate the effect of 15% and 35% carbamide peroxide gels as home and in-office bleaching agents respectively, on microhardness and surface topography of composite resin. In this in vitro study, a total of 75 disc shaped specimens were prepared from Z100 composite resin (3M) and randomly divided into three groups with following treatment designs: group 1, 370C distilled water, group 2, 15% carbamide peroxide, 6 hours/day for 3 weeks, group 3, 35% carbamide peroxide 30 minutes/week for 3 weeks. The microhardness (Vickers hardness) of samples was measured using Shimadzu set on three different points of each sample. 8 samples of each group were selected randomly to be assessed by scanning electron microscopy (SEM) for probable changes in surface topography. Data were analyzed using one way ANOVA and Duncan tests with p<0.05 as the level of significance. 15% carbamide peroxide group had the maximum amount of microhardness (84.59±1.87) and 35% carbamide peroxide group had the minimum (76. 14±1.77). Only the difference between home bleaching and control group was not statistically significant (P=0.24). The SEM assessing revealed no changes in surface topography. Based on the results of this study, in-office bleaching may decrease the microhardness of composite resin

Multiple systemic and local factors contribute to the incidence and progression of periodontal diseases. Osteoporosis is defined as changes in trabecular bone structure and probably as a systemic risk factor of periodontitis. Since both diseases are considered as major public health problems and affect numbers of adults the aim of this study was to investigate the relationship between osteoporosis and periodontal disease and the role of oral hygiene in this process. In this historical cohort study, 68 patients were selected from 111 individuals for whom femoral and hip BMD (Bone Mineral Density) with DXA (dual energy X-ray absorptiometry) procedure was performed and PI (Plaque Index) recorded. Cases were divided into four groups of 17 persons each as follow: osteoporotic with good oral hygiene (OH), osteoporotic with poor oral hygiene (OP) normal with good oral hygiene (NH), and normal with poor oral hygiene (NP). Clinical examinations including BOP (bleeding on probing),GR (gingival recession), PPD (probing pocket depth) and TL (tooth loss) was performed for all cases. Data were analyzed by two-way and four-way ANOVA test, with p<0.05 as the level of significance. Significant relation was observed between GR (P=0.045), and TL (P=0.050) with BMD independent of oral hygiene. Whereas such relation was not true for BOP and PPD (P=0.989). Our finding showed that osteoporosis can make patients more vulnerable to periodontal diseases by reducing trabecular bone mass and is related to gingival recession as well as tooth loss.

As central incisors have a prominent role in esthetics, appropriate preparation, considering natural tooth anatomy and proper planes have always been considered. The aim of this study was to determine the number of planes in labial surface of maxillary central incisors using image processing and mathematical analysis.

This pilot study was performed on 32 intact maxillary central incisors in dental students of Tehran university of medical sciences. Photographs were taken from profile view of each tooth by a digital camera. Images were processed and number of planes was obtained using SigmaScan Pro. version 5.00 software and a customized program. Data were analyzed by t-test and regression tests with p<0.05 as the level of significance.

96.9% of central incisors had three planes and 3.1% had two planes in labial surface. The angle between middle-cervical and middle-incisal planes showed statistically significant difference (p< 0.01).

Based on the results of this study, a few percentage of maxillary central incisors had two planes and most of them had three planes in their labial surfaces. Thus, considering three planes for restoring maxillary central teeth is closer to principles of tooth preparation and esthetics.

The utilization of information and communication technologies in medical librarianship would put librarians in new created conditions. Therefore، the aim of this study was to evaluate the effects of external factors on medical librarians'' attitudes toward their future professional situation. This was a cross-sectional study. All libraries and affiliated with ministry of health، and medical education were included in the study. The research consisted of all medical librarians working in the mentioned centers. Data was collected through questionnaires including two major parts and an additional section pertaining to personal information. From total of 1368 cases، 1001 answered to the questions. Statistical measurements consisted of frequency distribution، mean، percentage، measures of dispersion، correlation coefficient، and two tailed tests analyzed by SPSS software. P<0. 05 was considered as the limit of significance. The results showed that the mean score of external factors and attitude، were 3. 25 and 4. 18 respectively، at the scale of 5. There was a positive and significant relationship between external factors and attitude. Medical librarians did not consider the presence informaticians as a threat to their job security، and they have been able to adapt themselves to modern situations. Also، they were aware of the fact that if they can not succeed to match themselves with technological revolution، they will loose their jobs. Structural changes in staff and educational establishments are necessary to satisfy future needs and is a priority to improve the influence of external factors on medical librarians'' attitude toward the future of their profession.